We have a lot of graphs to go
through here, so let's get started. For the tests, I used an Audio Precision
AUX-002 switching amplifier filter, which reduces the amount of switching
frequency noise getting into the Audio Precision test instrument.

At 1 kHz and 5 volts output
into 8 ohms (a little over 3 watts, which is a typical listening power),
THD+N was only about 0.03%.

At 4 ohms, THD+N went up a bit,
but not significantly.

At 20 volts into 8 ohms (50
watts), THD+N was still low.

And at 4 ohms, still less than
0.04%.

IMD was also low, only 0.004%
with the standard SMPTE/DIN test, using a combination of 60 Hz and 2 kHz at
an output of 5 volts into 8 ohms. The test measures the resulting peaks
± 250 Hz around the upper test
frequency.

At 4 ohms, IMD went up,
expectedly, but it was still reasonably low.

Even at 20 volts output into 8
ohms, IMD was low, at 0.006%. As the chart indicates, the amplifier needed 1
volt input to produce the 50 watts output into 8 ohms.